Reproductive toxicity effects of 4-nonylphenol with known endocrine disrupting effects and induction of vitellogenin gene expression in silkworm, Bombyx mori.

4-Nonylphenol (4-NP) a known endocrine disrupting chemical is a persistent environmental contaminant. However, the mechanism of reproductive toxicity caused by 4-NP is still largely unresolved in invertebrates. In this study, Bombyx mori larvae were constantly fed 4-NP at concentrations ranging from 0.05 to 0.4gkg(-1), reproductive toxicity and induction of vitellogenin gene (Vg) expression were investigated in this organism which is an ideal lepidopteran model insect. The results showed that gonad development was retarded and maturity was decreased in both male and female pupae, while the sex ratio was unaffected by 4-NP exposure. In the 4-NP exposed animals, the corresponding egg yolk protein, vitellin, involved in energy reserves for embryonic development in oviparous animals, was present in the testis of male pupae, and the mRNA transcript of the Vg gene was detected in the fat body, a specific organ of Vg synthesis, which is normally silent in males. In addition, expression of the Vg gene was up-regulated in the fat body of female pupae and adults, while the protein was decreased in developing eggs. Furthermore, expression of the ecdysone receptor gene (EcR) in the ovaries of pupae was down-regulated, suggested that the transport of Vg from the fat body to developing oocytes was disturbed by 4-NP due to interference in the expression of EcR related to ecdysone activity.